The present invention relates to a pump for refrigerating systems, in particular for aeronautical applications.
As is known, axial or centrifugal pumps are used in refrigerating systems to compress the working fluid, which is generally freon. Such pumps have a pumping capacity ##EQU1## (where .DELTA.p is the obtainable pressure difference, .rho. is the density of the working fluid and V.sub.p is the impeller peripheral speed) which is relatively low, and therefore when high pressure differences are required in the refrigerating cycle, i.e. when the difference between the condensation temperature and the evaporation temperature is large, it is necessary to use multiple compression stages and/or pumps with an impeller driven at a high rotation rate. In refrigerating systems for aeronautical applications, used for example to refrigerate electronic components, high pressure differences are required. However, in this particular application it is necessary to provide very compact refrigerating systems in order to keep their weight within acceptable limits. Therefore the use of centrifugal or axial pumps is troublesome since the required number of compression stages and/or the use of high-speed electric motors considerably increases the overall weight of the refrigerating system.
Furthermore, in view of the variability of the demand of condensed fluid, said fluid very often enters the first compression stage while it is still liquid, causing the breakage or malfunction of the pump and entailing the use of additional devices, such as for example safety valves, with the effect of further increasing the weight of the system.